InSight – NASA mission to explore terrestrial planets
Although Mars is the focus of the InSight mission, it is actually about far more than exploring the Red Planet. Rather, the scientists want to contribute to research on terrestrial planets in general. In this case, terrestrial means a rocky planet consisting of an iron core, a rock mantle and a chemically differentiated crust. Mars is an ideal mission destination for this purpose, as it has shown precisely the correct degree of activity throughout its history. Firstly, it is large enough to have developed processes such as volcanism and tectonics but secondly, it is sufficiently small to preserve traces of this activity over billions of years.
These factors prompted NASA to select InSight for a mission to Mars as part of its Discovery Program.
InSight lifted off from Vandenberg Air Force Base on the Pacific coast of California at 05:05 local time on 5 May 2018, on board an Atlas V-401 launcher.
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(**). The InSight lander touched down on the surface of Mars on 26 November 2018, after a six-month journey through space..

InSight is the first mission to focus on a geophysical investigation of the Solar System. The instruments it carries are unusual for planetary research – a seismometer and a heat flow probe.
The seismometer
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(**) – that was built by the Institut de Physique de Globe de Paris (IPGP) in collaboration with Imperial College London, ETH Zürich and the Max Planck Institute for Solar System Research – will determine the inner structure of the planet and the size of its core. In contrast, the heat flow probe, which was developed under the leadership of the DLR Institute of Planetary Research in Berlin with the DLR Institute of Space Systems in Bremen and the Space Research Centre (Centrum Badań Kosmicznych; CBK) in Warsaw, will determine the temperature distribution in the planet’s interior. This will enable conclusions to be drawn regarding the chemical composition and activity of Mars. Direct measurements of these fundamental planetary parameters will be possible for the first time. Until now, they have only been inferred indirectly by means of gravitational field measurements.

In order to determine the heat flux of a planet, the temperature gradient in the subsurface must be measured.
In 1972, the astronauts on the Apollo 17 mission used percussion drills for this purpose, drilling boreholes up to three metres deep into the surface of the Moon. The disturbing influences of the Martian atmosphere mean that this depth is not sufficient for InSight. This is why the Heat Flow and Physical Properties Package (HP³) is designed to deliver temperature sensors to a depth of up to five metres – no easy task. To do this, HP³ uses an electromechanical ‘Mole’ that consists of a mechanical impact mechanism with which it drives the sensors into the ground in millimetre increments.

(*) In addition, HP³ is fitted with a radiometer that monitors the surface temperature at the landing site to support the heat flow measurements. The DLR scientists will then derive the planetary heat flow from the surface temperature data, as well as the temperatures in the subsurface.
The radiometer measures the infrared radiation from two areas on the surface that are at different distances from the lander (Field of View [FoV] 1 and 2 in image to the left, modified from https://link.springer.com/article/10.1007%2Fs11214-018-0531-4) in order to detect the temperature disturbances caused by the lander itself.
For technical reasons, the radiometer must be switched off from time to time, so the time axis of the soil temperature graphs shown above is irregular.

InSight is already the twelfth mission in the NASA Discovery Program, which focuses on cost-efficient projects with a comparatively low budget of around 500 million dollars. The hallmark of the Discovery missions is their strong focus on specific scientific questions. The Principal Investigator for the mission is Bruce Banerdt from the Jet Propulsion Laboratory (JPL), one of the most renowned Mars researchers in the USA. In addition to DLR, the French space agency CNES is also participating in the mission.